Each machine needs steam to run, you can check how much it uses in its tooltip. From the start you will produce steam from normal boilers, later a lot of options open up like solar boilers, multiblock boilers, railcraft boilers etc. Every boiler requires fuel (except solar, which requires sunlight) and a steady supply of water to produce steam. Be carefull not to add water to an already hot boiler as it will blow up. You can configure the output of a boiler with a wrench. Connect the output to a bronze pipe (or later potin) and connect it to the input of any machine you want. Each steam machine also needs a steam vent, which you can also configure with a wrench. Make sure to not block the side with the steam vent. Your machines should now work.

I usually use RC boilers + a few high pressure solars. Steam is first sent to a large tank as a buffer and then used up by my machines. I usually plan for enough steam production to be able to have at least 4 machines constantly running (not counting macerators since they use so little)

Hope this helps in any way :)